HAKS360

Hi, my octavia 1.6 tdi 5 speed manual 2013 has recently got 2 faults, I think they are related. When I start the car in the mornings the revs jump to 1800 rpm for a sec and then idles at 1100 for a min, then comes down to normal (750ish). It only does that the first time I start the car in the day. I do a lot of miles a day and realised my coolant temperature stays at 50 degrees even if I've driven all day. It sometimes goes upto 65 degrees for maybe a 30 secs and then goes down back to 50 degrees. Shouldn't if stay at normal optimal temperature at 90? Getting paranoid if my car is overhearing and not showing. But when I check the engine oil temperature it sit between 92-97 which looks normal. So I'm thinking if theres a problem with the coolant/ temperature sensor (does it have one) and where is it located, or maybe faulty thermostat if it has one again lol. Sorry for my long post and any help and guidance would be grateful.